1. Field of the Invention
This invention is directed to a layered metal chip used to produce a soldering connection for a power semiconductor module.
2. Description of the Related Art
Known chips for producing power semiconductor modules are usually soldered onto a support, e.g. a Direct Copper Bonded (“DCB”) substrate or a metallic plate, for heat dissipation purposes. Reference is made to Lugscheider E. et al. “Spannungsreduktion in Chip-DCB-Verbunden mittels Ausnutzung der intrinsischen Spannungseigenschaften von PVD-Metallisierungsschichten” [“Stress reduction in chip-DCB composite assemblies by means of utilization of the intrinsic stress properties of PVD metallization layers”], Verbundwerkstoffe and Werkstoffverbunde [Composite materials and materials composites], M. Schimmerer (ed.), 2005. Soldering connections may furthermore be necessary for producing electrical connections.
In order to produce the soldering connection, a layer assemblage formed from a plurality of metallic layers is provided on at least one side of the chip body. The layer assemblage is generally terminated by a noble metal layer, which prevents an undesired oxidation of the metallic layers situated therebeneath. A soldering layer is usually situated below the noble metal layer, which soldering layer, during the production of the soldering connection, at least partly melts together with the solder and, after solidification, fixedly connects the chip body to the support via further metallic layers connected to the soldering layer.
During the production of chip-DCB composite assemblies, in particular, it may be necessary to carry out a plurality of soldering operations. In this case, it may happen that the layer assemblage produced from the metallic layers, in particular, is heated repeatedly to a temperature of from about 200 to about 250° C. When a soldering connection that has already been produced is reheated, it can happen that a new melt forms from the soldering layer and the solder advances in the direction of the chip body and penetrates through further metallic layers of the layer assemblage in an undesirable manner. Consequently, voids or pores can form within the layer assemblage. Such voids or pores weaken the mechanical strength and/or electrical conductivity of the soldering connection.